1. Field of the Invention
The invention relates to an impression tray with a concave tray body for taking an impression of at least one jaw part, in which at least one implant body is situated, which body has a receiving aperture into which an impression post may be inserted, it being possible to fill the impression tray with a free-flowing hardenable impression material to produce a mould for a model of the jaw part.
2. Description of the Related Art
As is known, when one or more teeth are lost replacement roots, what are known as implants, are implanted into the jaw. These supports that are anchored in the jaw form the stable base for new, secure teeth. The size and shape of an implant is guided by the individual preconditions of the jaw of the patient being treated. One precondition for tooth implantation is a minimum jaw bone substance.
Since implants are osseo-integrated (anchored to a bone) and, in contrast to natural teeth, do not—ideally—have even the slightest inherent movement, when constructing a plurality of implants an optimally exact three-dimensional reproduction of the position of the individual implants is particularly important.
The replacement produced in a dental laboratory can only be successfully incorporated in the oral cavity without stress if the clinical situation is transferred exactly to a model. While a precise impression is not a sufficient condition it is a necessary one for implantological-prosthetic care.
The aim of any impression is thus the exact dental model. It is used for diagnosis, planning and treatment purposes as well as a work basis for the dental technician and should be an exact copy of the structures that are in the oral cavity.
The part of an implant system that is countersunk into the bone is either called an implant body or simply an implant. Once it has been introduced into the bone the hollow implant body is provided with a cover screw. The gums are then stitched over the implant body. Following a healing phase of several months' duration, the doctor then exposes the implant body again, removes the cover screw and temporarily screws or inserts an impression post in its place.
After a healing period of 10 to 14 days, the impression may be taken over the impression post by means of an individually shaped impression tray in order to subsequently produce the crown, bridge or prosthesis. The impression post is then replaced for a few days by healing abutments. The definitive new teeth are not secured directly to the implant bodies, but to implant superstructures, however. Implant superstructures bridge the thickness of the gums, so the gums cannot be squashed between implant body and prosthesis. The healthy gums attach to these implant superstructures as to a natural tooth. The prosthesis accordingly supported by the implant abutment and implant body is called a superconstruction and is secured by filling screws or other fastening principles to the individual implant bodies.
To determine the three-dimensional position of the implant body and to transfer this to the final laboratory model, the following steps are carried out:
1. Taking a negative impression of a jaw, or jaw part, by means of a standardised impression tray, a cover screw, arranged inside the impression tray, being screwed into the implant body,
2. a) Producing a first laboratory model using the negative impression,
                b) Producing an individual impression tray using the laboratory model, the impressions of the cover screw being drilled in order to allow subsequent passage of an impression post through the impression tray at this location.3. a) Removing the implant cover, anchoring a multi-part impression post in the jaw by latching or screwing,        b) Filling the impression tray with impression material in the region of the hole,        c) Placing the impression tray on the jaw, with the impression post surrounded by the impression material projecting through the hole and beyond the impression tray,        d) Once the impression material has hardened, unscrewing, removal or detachment of the impression post and removal of the impression tray with the impression material, an impression post sleeve that laterally surrounds the impression post remaining in the impression material.4. a) After disinfecting the impression tray, producing a second laboratory model, with a laboratory implant body being placed on or screwed to the impression post sleeve in the impression material by means of a laboratory impression post. The material for moulding the second laboratory model is injected onto the laboratory implant body. The remaining negative mould of the laboratory model is filled with model materials, such as plaster of Paris or plastics material. After the model materials have hardened the impression post retaining screw or the impression post retention pin can be detached again. The impression tray can be removed from the model.        b) Choosing and using a suitable implant abutment in the laboratory implant body of the second laboratory model, production of the dental prosthesis.        
The repositioning technique may be used as an alternative. The major advantage is that the patient is spared a treatment appointment for production of the individual impression tray. A further advantage is also that the costs that occur during production of the individual impression tray with respect to expenditure of material and time do not apply in the case of the repositioning technique with ready-made trays.
However, a drawback of this technique is that its application is error-prone and has also been proven to be less precise compared with the above-described “pick-up” technique since, inter alia, the channel-like impression of the impression post required for the three-dimensional repositioning of the position of the implant body in the impression material may only be replaced by shallow and imprecise impressions of impression elements and hence leads to unsatisfactory results for the doctor and primarily the patient. Repositioning of the impression tray also leads to significant movements in the impression material, so the precision of the subsequent model decreases.
Guillaume et al disclose in U.S. Pat. No. 6,468,078 B2 a ready-made tray comprising a plurality of removable segment seals. Depending on the position of the impression post—which is constructed as a sleeve—it is proposed that the segment seal located thereabove be removed and the material, which is still covering the impression post and a screw fixing the post to the implant body, subsequently be removed until at least the screw head is completely exposed. After the impression material in the ready-made tray has hardened the screw should be detached. The impression post remains in the impression material moreover and is used to fix the laboratory implant using the impression screw.
When using the proposed impression tray however the process of removing impression material over the screw, which process on its own is already complex but, owing to hardening of the impression material, is also limited in terms of time, may lead to considerable problems. The exact position of the screw must also firstly be ascertained and then the screw head freed of the impression material, at least to the extent that the screw may be engaged using a screwdriver or the like. A further drawback is that the interplay between impression post and positioned impression tray may no longer be checked and corrected if necessary since the impression post can no longer be seen in its position relative to the impression tray.